JP6437093B2 - Magnetometer using membrane - Google Patents

Description

  The various exemplary embodiments disclosed herein generally relate to an electronic device or device component having a metal membrane that measures and reports the orientation of the device with respect to a magnetic field.

  A multi-degree-of-freedom inertial measurement device (ie, IMU) is an electronic device or device component that measures and reports device speed, orientation, and gravity, and is a portable device component for navigation and orientation sell. One embodiment of an IMU includes multiple packages or multichip combinations of accelerometers, gyroscopes, altimeters, and compass or magnetometers that are often integrated into a microelectromechanical system (MEMS).

  IMU's miniaturization, integration, standardization, and cost reduction will broaden its use as a compass and magnetometer in portable applications such as smartphones, dedicated navigation, and location-based devices. In some cases, expensive materials are required, unnecessarily increasing the bill of material (BOM) cost of such equipment.

  In view of the current desire for a compact, low cost, high sensitivity compass, an overview of various exemplary embodiments is presented. In the following summary, some simplifications and omissions may be made to highlight and introduce some aspects of the various exemplary embodiments, but they do not limit the scope of the invention. The following section provides a detailed description of preferred exemplary embodiments suitable to enable those skilled in the art to make and use the inventive concepts.

  Various exemplary embodiments relate to a magnetometer device for measuring vibration frequency, wherein the magnetometer device is connected to a feedthrough loop including an amplifier and a voltage bias connected to a first input of a metal membrane, and to a membrane output. A fixed plate having a first fixed plate output connected to the membrane ground and the second input of the amplifier, wherein the fixed plate is physically separated from the metal membrane, while the Lorentz force causes the metal membrane to Connected to the fixed plate, the physical separation of which depends on the angle of the magnetic field with respect to the direction of the current, the second fixed plate output sensitive to the Lorentz force, and the second fixed plate output, based on the Lorentz force A circuit for calculating the angle of the magnetic force. In an alternative embodiment, the metal membrane includes a continuous metal sheet. In some embodiments, the metal membrane further includes a continuous metal winding that extends in parallel lines from the membrane input to the membrane output. In yet another exemplary embodiment, the metal membrane further includes an insulator sheet with embedded metal windings.

  In some implementations, the angle of magnetic force is given by the angle of the magnetic field relative to the direction of the current.

  In some embodiments, the feedback loop is configured to pass alternating current through the metal membrane.

  In some embodiments, the direction of the current is given by the direction of the alternating current that is passed through the metal membrane by the feedback loop.

  In some implementations, the direction of current is given by the direction of current between the first input and the membrane output of the metal membrane.

  In some embodiments, the magnetometer device, in particular the circuit, is configured to measure the vibration frequency and / or shift of the vibration frequency of the metal membrane.

  In some implementations, the vibration frequency shift is generated by a magnetic field.

  In some implementations, the magnetometer device, in particular the circuit, is configured to calculate the angle of the magnetic force based on the vibration frequency and / or the shift of the vibration frequency.

  Various exemplary embodiments relate to a magnetometer device for measuring vibration frequency, the magnetometer device being connected to a feedthrough loop including an amplifier, a voltage bias connected to a first input of a metal membrane, and a membrane output. A fixed plate having a first fixed plate output connected to the membrane ground and the second input of the amplifier, wherein the fixed plate is physically separated from the metal membrane while the Lorentz force causes the metal membrane to A fixed plate connected and different in physical separation depending on the angle of the magnetic field with respect to the direction of the current, a second fixed plate output sensitive to Lorentz force, and a second fixed plate output connected to the second fixed plate output, the magnetic field based on the Lorentz force And a circuit for calculating the angle.

  In some implementations, the angle of the magnetic field is given by the angle of the magnetic field relative to the direction of the current.

  In some implementations, the magnetometer device, in particular the circuit, is configured to calculate the angle of the magnetic field based on the vibration frequency and / or the shift of the vibration frequency.

  In some embodiments, the metal membrane has an equivalent electrical inductance proportional to the mechanical mass of the metal membrane, an equivalent capacitance proportional to the mechanical stiffness of the metal membrane, and an equivalent electrical capacitance proportional to the mechanical damping of the metal membrane. With resistance. In some embodiments, the amplifier has a current controlled voltage source. In some alternative embodiments, the current controlled voltage source has gain. In some embodiments, the fixation plate has the same size as the metal membrane. In an alternative embodiment, the metal membrane is free standing. In some embodiments, the securing plate is secured to the substrate. In some other embodiments, the fixed plate is fixed to the wafer.

  Various exemplary embodiments relate to a method for measuring the orientation of a device, the method comprising: passing an alternating current through a metal membrane; measuring a shift in vibration frequency within the metal membrane; and shifting the vibration frequency. Calculating an angle of the external magnetic field with respect to the metal membrane based on the current direction. An alternative embodiment further includes creating a feedback loop that vibrates the metal membrane. In some embodiments, the vibration is close to the mechanical resonance frequency of the metal membrane.

  In some implementations, the angle of the external magnetic field relative to the metal membrane corresponds to the angle of the external magnetic field relative to the direction of the alternating current flowing through the metal membrane.

  In some alternative embodiments, creating the feedback loop comprises creating a capacitive displacement current, sending the capacitive displacement current to an amplifier, amplifying the capacitive displacement current with the amplifier, Sending the amplified current as a voltage to the metal membrane. In some alternative embodiments, the method further includes generating a bias voltage between the metal membrane and the fixed ground plane. In some embodiments, the stationary ground plane is located a short distance from the metal membrane. In an alternative embodiment, the fixed ground plate has the same ratio as the metal membrane.

  In some embodiments, calculating the angle of magnetic force further includes counteracting effects that may detune the vibration frequency. In an alternative embodiment, the step of counteracting includes subtracting the vibration frequency in one or more current directions. Alternative embodiments of the method further include filtering interference from vibrations of the metal membrane. In some embodiments, filtering the interference includes measuring the frequency of the oscillator for a sufficient period of time.

  Various exemplary embodiments relate to a magnetometer device that measures the orientation of the device, the magnetometer device configured to cause an alternating current to flow through the metal membrane and vibrate the metal membrane, including an oscillator including a metal membrane and a feedback loop. And the vibration frequency shift generated by the feedback loop and the metal membrane is measured, and the angle of the external magnetic field with respect to the direction of the current is calculated based on the vibration frequency shift and the current direction. And a processor. In some alternative embodiments, the vibration is close to the mechanical resonance frequency of the metal membrane. In an alternative embodiment, the feedback loop further includes an amplifier, further creates a capacitive displacement current, sends the capacitive displacement current to the amplifier, amplifies the capacitive displacement current by the amplifier, and generates the amplified current. It is configured to be sent as voltage to the metal membrane.

  In some alternative embodiments, the magnetometer device further comprises a fixed ground plate, and the device is further configured to generate a bias voltage between the metal membrane and the fixed ground plate. In other embodiments, the stationary ground plane is located a short distance from the metal membrane. In some form embodiments, the fixed ground plane has the same ratio as the metal membrane. In an alternative embodiment, in calculating the angle of the external magnetic force, the processor is further configured to counteract the vibration frequency detuning effect. In some alternative embodiments, the processor is further configured to subtract one or more current direction vibration frequencies when negating the vibration frequency detuning effect.

  In an alternative embodiment of the magnetometer device, the processor is further configured to filter interference from vibrations of the metal membrane. In other embodiments, the processor is further configured to measure the frequency of the oscillator for a sufficient period of time.

  In some embodiments, the processor is connected to a stationary ground plane to measure vibration frequency shifts.

  Thus, various exemplary embodiments are particularly sensitive, small and cost effective to the angle of the magnetic field by measuring the displacement of the metal membrane subjected to the force generated by the effect of the magnetic field. Clearly, it allows for a high device.

  For a better understanding of various exemplary embodiments, reference is made to the accompanying drawings.

FIG. 5 is a diagram illustrating the behavior of an exemplary free-standing metal membrane when mechanically resonated. FIG. 2 shows an exemplary alternative embodiment of the membrane of FIG. It is a figure which shows the cross section of the membrane of FIG. FIG. 5 is a diagram illustrating the effect of an exemplary current direction on an exemplary magnetic field on vibration frequency. FIG. 2 illustrates an exemplary circuit that is electrically equivalent to the oscillator illustrated by FIG. 1. It is a figure which shows the plot of the admittance of the resonator membrane in an imaginary plane. It is a figure which shows the cross section of the coil | winding embedded in the metal membrane and the board | substrate. FIG. 4 is a cross-sectional view of a membrane and a circuit for outputting a sensor reading and calculating a magnetic field based on the displacement of the membrane. FIG. 8 shows an exemplary circuit equivalent to the membrane and circuit of FIG.

  In view of the above, measuring the orientation of the device with respect to a magnetic field using materials that can be used to implement multiple sensors that are inexpensive and conform to smaller shape factors and measure various states Is desirable.

  MEMS sensors using Lorentz force known in the art, such as Hall effect sensors and anisotropic magnetoresistive (AMR) sensors, are used to measure the mechanical movement of a MEMS structure by Lorentz force acting on a conducting conductor in a magnetic field. (Note that the conductors of known Lorentz force sensors are composed of semiconductor material). In other words, these sensors measure mechanical displacement. In various applications, the mechanical structure is often resonated to obtain a maximum output signal. Piezoresistance and electrostatic conversion may be used to electronically detect the direction of the magnetic field. The piezoresistive effect is the change in electrical resistance of a semiconductor or metal when mechanical strain is applied.

  Because of the need for a magnetometer that is easier to manufacture at a lower cost, for measuring the in-plane orientation of the earth's magnetic field using standard non-magnetic complementary metal oxide semiconductor (CMOS) compatible materials The system and method are described. For example, the system described herein may be based on a mechanical vibration frequency shift measurement of a vibrating metal membrane. This differs from currently known magnetometer applications that use Hall effect or AMR sensors, which, due to their required mechanical properties (eg, including physical displacement measurements and semiconductor manufacturing) It is assembled separately from other sensors. In addition, magnetic sensors can be manufactured using the same materials as currently existing MEMS sensors (such as pressure sensors) mounted on CMOS, with a free-standing membrane, so that the magnetic sensor is a process complexity or associated cost. Without being increased, they may be combined on a single CMOS chip that forms part of the inertial measurement device. This can include multiple functions (eg, barometric pressures (eg, in altimeters) that may be combined to perform 3D positioning, such as may be included in portable devices or other handheld devices, navigation devices, or vehicles. ) And detect physical orientation)) for various applications such as one component in a sensor package.

  In self-supporting metal membranes, mechanical vibrations can be caused using a combination of Lorentz force and electrostatic force. The frequency can be measured with high accuracy. The Lorentz force depends on the angle between the in-plane magnetic field and the current passed through the metal membrane. The change in angle causes a change in the Lorentz force, thus causing a slight but detectable detuning of the vibration frequency. By measuring the oscillation frequency shift, it is possible to determine the orientation of the earth's magnetic field relative to the magnetometer.

  If the metal membrane has the same dimensions and physical properties as the membrane used to detect other physical ambient conditions such as atmospheric pressure, the same membrane may be used to detect both conditions. For example, the same physical sensor as the altimeter and magnetometer may be used using time multiplexing. Combining functions on a single structure not only saves manufacturing and material costs and simplifies the manufacturing process, but also reduces the shape factor.

  In addition, inductors and other magnetic field generating elements may be easily integrated on the underlying CMOS, and the magnetometer can be calibrated and fine tuned in the field using electrical stimulation. Because the necessary components can be integrated, the calibration procedure may be repeated in the field, thereby compensating for sensor drift caused by aging and other factors. Furthermore, since the pressure and temperature can be measured in the immediate vicinity of the magnetometer, the lateral sensitivity of the magnetometer to a force other than the magnetic field such as atmospheric pressure and temperature can be accurately known and suppressed by calibration.

  Referring now to the drawings in which like reference numbers indicate like components or steps, the broad aspects of the various exemplary embodiments are disclosed.

FIG. 1 illustrates the behavior of an exemplary freestanding metal membrane 110 when mechanical resonance is caused by a combination of Lorentz force F _lor and electrostatic force F _el . The membrane-based magnetometer 100 may include the membrane 110 _in an oscillator loop (including i _in , C _ft , V, membrane 110, ground 150, i _out , transimpedance amplifier TIA, and ground 140). The Lorentz force F _lor may be generated by passing a current, such as an alternating current i _in 120, combined with the geomagnetic field B through the membrane 110. Since the Lorentz force is linear with respect to the current density, a metal membrane 110 having a low resistance and a higher current density is used to provide a greater Lorentz force (eg, compared to a semiconductor with a higher resistance). Can be generated.

ここで、ｋ_bはボルツマン定数であり、Ｔはメンブレン１１０の周囲の絶対温度であり、γはメンブレン１１０の減衰係数（まわりの空気と相互作用するとき）であり、これらに、測定が行われた帯域幅Δfを掛けたものであり（ホワイトノイズ現象と同様に帯域幅が係数である）、これはセンサ計算に考慮されうる。信号対雑音比が大きいほど磁気計の感度が高くなる。信号対雑音比は、システムの機械的ノイズＦ_noiseに対して大きいローレンツ力Ｆ_lorを生成することによって最大化されることがあり、できるだけ小さくなければならない。Ｆ_noiseは、減衰係数γを最小にすることによって最小化でき、これは、メンブレン１１０の品質係数Ｑを最大化することによって達成されうる。ローレンツ力Ｆ_lorを生成するのに必要な電力Ｐは、メンブレン１１０の上で送られる電流ｉ_inの関数であり、メンブレンの電気抵抗Ｒ（Ｐ＝ｉ_inｉ^２×Ｒ）であり、金属の抵抗が半導体の抵抗より小さいので、金属メンブレン１１０に大きいローレンツ力Ｆ_lorを生成するために必要な電力が少なくなる。更に、長さｌを大きくするとローレンツ力Ｆ_lorが大きくなる。メンブレン１１０の寸法を大きくせずに長さｌを大きくすることは、図２Ａに示された例示的な代替実施形態で達成されてもよい。 Exemplary metal membranes, such as membrane 110, have several advantages over semiconductor-based Lorentz force sensors known in the art. In its simplest terms (more detailed calculations will be described later), the Lorentz force F _lor is the product of the length l of the membrane 110, the magnetic field B, and the sine of the angle α between the direction of the magnetic field and the direction of the current. ( _Flor = l × i _in × B × sin α) However, since the membrane is a mechanical system, random mechanical noise affects the movement of the membrane 110. This random noise may be represented by the following force F _noise .

Here, k _b is the Boltzmann constant, T is the absolute temperature around the membrane 110, γ is the attenuation coefficient of the membrane 110 (when interacting with the surrounding air), and these are measured. Multiplied by the bandwidth Δf (the bandwidth is a coefficient as in the white noise phenomenon), which can be taken into account in sensor calculations. The greater the signal to noise ratio, the higher the sensitivity of the magnetometer. The signal to noise ratio may be maximized by generating a large Lorentz force F _lor for the system mechanical noise F _noise and should be as small as possible. F _noise can be minimized by minimizing the attenuation factor γ, which can be achieved by maximizing the quality factor Q of the membrane 110. The power P required to generate the Lorentz force F _lor is a function of the current i _in sent over the membrane 110, is the membrane electrical resistance R (P = i _in i ² × R), Since the resistance is smaller than the resistance of the semiconductor, less power is required to generate a large Lorentz force F _lor on the metal membrane 110. Further, when the length l is increased, the Lorentz force F _lor is increased. Increasing the length l without increasing the size of the membrane 110 may be achieved in the exemplary alternative embodiment shown in FIG. 2A.

FIG. 2A shows an exemplary alternative embodiment 210 of the membrane 110. In some embodiments, the metal membrane 210 may include a metal tracer 220 that can be embedded in the membrane 110 as shown in FIG. 2B instead of the membrane 110 comprising a continuous metal sheet. Tracer 220 (constituting the coil extend in one continuous around the membrane) output v _in is implemented as a metal wire / coil extending in series from the side to the output ground 150, constitutes the membrane 210 together May be.

  As described above, the Lorentz force increases and the power dissipation decreases as the current increases. Therefore, it is important that the wire is long in order to keep the electrical resistance low, and in order to extend l while keeping R low. Metal windings may be used. Most sensors that utilize Lorentz force use doped silicon having a resistivity of about 1 mΩ · cm, which is 1000 times that of a metal winding of about 1 μΩ · cm (micro ohm centimeter). Is more efficient in terms of signal to noise ratio and power dissipation. Furthermore, by using multiple tracer windings rather than a single sheet, the wire length is maximized, resulting in an increased total resistance of the tracer wires and a supply voltage (membrane 210 is connected to the CMOS). 1 volt across multiple tracer lines with a higher resistance (eg,> 1 kilohm) than a sheet with a low resistance (eg, 0.1 ohm). It is likely to consume an exemplary input current of 1 milliwatt from less than the supply voltage. Alternatively, a v-converter can be used to reduce the current on the membrane sheet, but this configuration increases the complexity and cost that can be avoided.

In the exemplary membrane 210, the trace width w _t may be 2 μm, the spacing between adjacent tracers may be 0.5 μm, the number of traces N may be 90, and the width w and length l of the membrane may be 220 μm. The Lorentz force F _lor is shown to be perpendicular to the tracer winding 220, where the magnetic force B is perpendicular to the winding 220. The metal winding 220 may be embedded in the insulator sheet 230 to form the membrane 210. Since the tracer number N is 90, the effective length l _wire used to create the Lorentz force F _lor is N times the width of the membrane (ie 90 × 220 μm), (in the simple membrane of FIG. The calculation of the Lorentz force (expressed as F _lor = l × i _in × B × sin α) is multiplied by N, so that F _lor = N × l × i _in × B × sin α. Lorentz forces in membranes that use wires are higher than single metal membranes. Here, l is limited by the length of the membrane sheet.

An exemplary metal membrane with 2 μm lines separated by 0.5 μm, with measurements similar to those shown in FIGS. 1, 2A and 2B, has a resonant frequency of 878.956 kHz, 223. A quality factor Q of 8, a mass m of 6.26 ⁻¹⁰ kg, a spring constant k of 1.914 ⁴ N / m, and a damping coefficient γ of 1.53 ⁻⁵ Ns / m, where Q = sqrt (k It can be expected to have (calculated from Q, m and k) for m) / γ. Note that a continuous metal membrane and a membrane with an etch toy wrench covered by an insulator to form a tracer winding can be expected to have relatively similar mechanical properties. As described above, the sheet resistance may be 0.1Ω, and the total resistance of the electric wire is 1 kΩ.

As shown in FIG. 1, when the current i _in has a component 120 perpendicular to the magnetic field B and both the current i _in and the magnetic field B are directed in the plane of the membrane 110, the Lorentz force F _lor is , Oriented perpendicular or perpendicular to the membrane 110. The electrostatic force F _el may be generated by the AC voltage V _in and the DC bias voltage V between the metal membrane 110 and the fixed ground plate 130 located at a slight distance from the metal membrane 110 (where, (Note that ground plate 130 and membrane 110 are separated by a small distance in the absence of current). Since the metal membrane 110 has a finite electrical resistance, the AC voltage v _in is caused by a voltage drop caused when the AC current i _in is flowed to the membrane 110. Note that _{in the} exemplary compass 100, one of the membranes 110 is grounded 150, so the voltage drop across the membrane 110 is vin.

In addition, an alternating current i _in 120 is passed through the free-motion membrane 110, which may include a metal plate that moves relative to the fixed ground plate 130 (which may be fixed to the substrate or wafer), thereby causing the transimpedance amplifier TIA. transmitted signal by capacitive displacement current i _out is applied is, the signal is fed back to the free-standing metal membrane as a voltage v _in, resulting feedback loop is created by vibrating the freestanding membrane at a frequency close to the mechanical resonance frequency Let In the case where the current i _in is an alternating current having a frequency that matches the resonance frequency of the membrane 110, an alternating Lorentz force F _lor is generated by mechanical resonance of the membrane 110 in the direct current magnetic field. The frequency shift is caused by the interaction between the Lorentz force F _lor and the electrostatic force F _el , and the electrostatic force is generated by the electrostatic force between the membrane 110 and the ground plate 130.

  Since the vibration frequency depends on the loop phase depending on the magnitude of the Lorentz force, the vibration frequency depends on the magnetic field being measured. Therefore, by measuring the oscillation frequency, the direction of the magnetic field with respect to the AC drive current can be obtained, and the direction of the geomagnetic field can be determined.

FIG. 3 shows the effect of the example current i _{in on} the geomagnetic field B on the vibration frequency _in the direction 120 with respect to a plan view of an example free-standing membrane such as the membrane 110 of FIG. As can be seen in FIG. 3, all 360 ° angle identifications i _y , i _xy , i _x , i _yx, etc. (turn around and return to i _y ) cause the current i _in to flow _{in the} membrane 110 in various directions. Sometimes it can be established. Note that because the geomagnetic field B has a relatively constant magnitude within a given area on the surface of the earth, the only variable that changes when the device rotates is the angle α. The current i _in flowing in the x direction 120 causes a detuning of the vibration frequency different from the current flowing _in the y direction because the magnitude of the Lorentz force is different between the two currents. Similarly, the frequency detuning due to the current 120 flowing in the x = y diagonal is different from the current 120 flowing in the x = −y diagonal. By determining the reference frequency, comparing those frequencies in different current directions and measuring the difference between such different detuning frequencies, the angle α is resolved over 360 ° and the magnetic field is fully identified . Therefore, the determination of the magnetic field based on frequency measurement is expected to achieve higher resolution and accuracy than the determination based on mechanical measurement. In addition, vibration frequencies in various current directions can be subtracted to counteract undesirable effects that can cause vibration frequency detuning, such as frequency shift caused by aging materials, temperature, and changing bias voltage. Also good.

Interference caused by the electric field, applied to the input voltage v _in or output current i _out, adding noise to the oscillator in the form of noise oscillation amplitude or phase. If this noise is random, it can be filtered by measuring the frequency of the oscillator for a sufficient period of time, as described below. Permanent shifts in vibration frequency or phase are less likely than random interference, but can be filtered by calibration techniques. In some embodiments, the electromagnetic interference (EMI) filtering method may be to ground a board facing the outside world. In FIG. 1, the ground plate 130 is connected to a virtual ground 140, but the configuration of FIG. 1 may be modified so that the membrane 110 is grounded (via TIA) to suppress EMI. Please be careful. Note that the CMOS chip containing magnetometer 100 may be isolated and shielded from EMI using a ground plane or other method.

  Also, when the magnetometer 100 is duty cycled (periodically or only turned on as needed), the mechanical inertia of the membrane requires a short “warm-up” delay before reading reliably. Please note that. This delay may be undetectable by the user in the exemplary embodiment as it may be 1 millisecond (eg, quality factor Q × period, where, for example, Q = 100, frequency = 100 kHz), but some Applications may require frequency readings. Thus, if a measurement period over a longer period (eg, 1 second) is required, the device may be duty cycled, but if a measurement every 1 millisecond is required or required, the device May be on for as long as needed (because otherwise the mechanism is too slow to accommodate the duty cycle and make the necessary measurements more accurate).

  To calculate the in-plane orientation of the geomagnetic field, a model can be determined that describes the relationship between the vibration frequency of a membrane, such as the exemplary membrane 110, and a reference frequency as a function of the magnetic field direction. As described above, the Lorentz force is equal to the outer product of the current and the magnetic field.

ここで、ｌがメンブレンの長さ、Ｂが磁場の大きさ、αが磁場と電流ｉ_inの方向の間の角度である。したがって、ローレンツ力Ｆ_lorは、電流ｉ_inが流されるメンブレン１１０の長さｌと、電流ｉ_inと磁場Ｂの間の角度Ｂｓｉｎαとに比例し、ここで、電流ｉ_inは、周波数ｊωｔを有する交流電流であり、磁場Ｂは、直流磁場である（交流電流と直流磁場の積が交流ローレンツ力を生成する）。メンブレン１１０が、連続金属シートの代わりに、メンブレン１１０を構成する埋め込み金属トレーサを含む実施形態では、式（１）は、メンブレン１１０を通る金属線の数に対応する整数Ｎが掛けられる。したがって、前述のように、連続金属シートではなく複数のトレーサＮを使用することによって、ローレンツ力Ｆ_lorはＮ倍になり、センサ感度がＮ倍になる。 The time alternating Lorentz force F _lor acting on the exemplary membrane 110 may be described as:

Here, l is the length of the membrane, B is the magnitude of the magnetic field, and α is the angle between the direction of the magnetic field and the current i _in . Accordingly, the Lorentz force F _lor is proportional to the length l of the membrane 110 that current i _in is passed through, in the angle Bsinα between current i _in and the magnetic field B, where the current i _in has a frequency jωt AC current and magnetic field B is a DC magnetic field (the product of the AC current and the DC magnetic field generates an AC Lorentz force). In embodiments where the membrane 110 includes an embedded metal tracer that constitutes the membrane 110 instead of a continuous metal sheet, Equation (1) is multiplied by an integer N corresponding to the number of metal lines passing through the membrane 110. Therefore, as described above, by using a plurality of tracers N instead of a continuous metal sheet, the Lorentz force F _lor is increased N times, and the sensor sensitivity is increased N times.

ここで、係数１／２は、メンブレン１１０の長さ全体にわたって電圧が降下することを考慮し（前述のように接地１５０により）、平均電圧は、全電圧降下の２分の１になる（換言すると、計算は、電圧がメンブレン１１０の中心の電圧と等しいと仮定する）。 The voltage v _in and the current i _{in in the} membrane 110 are related by Ohm's law (see the following equation (2)).

Here, the factor 1/2 takes into account that the voltage drops over the entire length of the membrane 110 (via ground 150 as described above) and the average voltage is one-half of the total voltage drop (in other words, The calculation then assumes that the voltage is equal to the voltage at the center of the membrane 110).

この式は、前の２つの式（１），（２）から導き出される。メンブレン１１０と接地板１３０の間の静電力Ｆ_elは、電圧に関して表されるため、メンブレン１１０上の平均交流電圧は、次式（４）によって表されるような静電引力を引き起こす。

ここで、Ｖが静的バイアス電圧、ε₀が誘電率、Ａ＝ｌｗがメンブレン１１０の面積、及びｇがメンブレン１１０と接地板１３０の隙間の距離である。 Lorentz force F _lor may be expressed as the following equation (3) with respect to the voltage v _in.

This equation is derived from the previous two equations (1) and (2). Since the electrostatic force _Fel between the membrane 110 and the ground plate 130 is expressed in terms of voltage, the average AC voltage on the membrane 110 causes electrostatic attraction as expressed by the following equation (4).

Here, V is the static bias voltage, ε ₀ is the dielectric constant, A = 1w is the area of the membrane 110, and g is the distance between the membrane 110 and the ground plate 130.

ここで、以下式は、メンブレンの面から外向きの速度である。

The output current i _out is related to the speed of the membrane 110. This is a standard expression in many MEMs, where a displacement current i _out occurs when the capacitance changes under a bias voltage. Membrane deflection causes capacitance changes and displacement currents that may be expressed as:

Here, the following expression is the speed outward from the surface of the membrane.

また、この式（６）は、メンブレンに加わる力、ローレンツ力Ｆ_lor及び静電力Ｆ_elと釣り合い、式（３）、（４）、（５）及び（６）を組み合わせることによってインピーダンスとして電気的条件で書き換えてもよく（入力電圧ｖ_inと出力電流ｉ_outとの関係）、その結果、次式（７）が得られる（換言すると、入力電圧ｖ_inは、インダクタンスによって生じるインピーダンス、抵抗によって生じるインピーダンス、及びキャパシタンスによって生じるインピーダンスと等価である）。

Furthermore, the self-supporting membrane 110 is added to the equation of motion (the product of the mass 110 of the membrane 110 multiplied by the acceleration and the product of the attenuation γ of the membrane 110 and the velocity), and further multiplied by the spring force k of the membrane 110 and the displacement x. May be regarded as a mass spring system determined by the following equation (6).

This equation (6) is balanced with the force applied to the membrane, the Lorentz force F _lor, and the electrostatic force F _el, and is electrically expressed as impedance by combining the equations (3), (4), (5), and (6). may be rewritten under the condition (relationship between the input voltage v _in and the output current i _out), as a result, the following equation (7) is obtained (in other words, the input voltage v _in the impedance caused by the inductance, caused by the resistor Impedance and equivalent to the impedance caused by the capacitance).

ここで、静電結合係数ηと磁気離調係数δは、次式（１１）と次式（１２）として表されてもよい。

δが磁場の関数であり、したがって、磁場Ｂ＝０、δ＝０、ならびにＬ_B、Ｃ_B及びＲ_Bが一定値の場合、したがって、磁場Ｂ≠０でｓｉｎα≠０の場合（電流ｉ_inと磁力Ｂが平行の場合、ローレンツ力Ｆ_lorがなくなるので）、Ｌ_B、Ｃ_B及びＲ_Bの値が磁場の関数として変化することを理解されよう。したがって、メンブレン２００がコンパスとして使用される場合、次式（１３）は、地球磁場Ｂと、前述のように装置が回転するときに変化する変数αとに基づくことがあるので適切になり、したがって、振動周波数δのシフト値の変化を測定することによって、値αの変化を使用して方向を決定できる。他の磁場Ｂの測定も可能である。

L _B , C _B and R _B (mechanical mass, stiffness and damping) are given by the following formula (8) (inductance is proportional to mass m), following formula (9) (resistance is proportional to damping γ), and It may be expressed as the following equation (10) (capacitance is inversely proportional to the spring force k).

Here, the electrostatic coupling coefficient η and the magnetic detuning coefficient δ may be expressed as the following expressions (11) and (12).

δ is a function of the magnetic field, so if the magnetic field B = 0, δ = 0, and L _B , C _B and R _B are constant values, then the magnetic field B ≠ 0 and sin α ≠ 0 (current i _in It will be appreciated that the values of L _B , C _B and R _B will change as a function of the magnetic field, since the Lorentz force F _lor will disappear if the magnetic force B and the magnetic force B are parallel. Thus, when the membrane 200 is used as a compass, the following equation (13) is appropriate because it may be based on the geomagnetic field B and the variable α that changes as the device rotates as described above, and therefore By measuring the change in the shift value of the vibration frequency δ, the change in the value α can be used to determine the direction. Other magnetic field B measurements are possible.

FIG. 4 shows an exemplary circuit 400 that is the electrical equivalent of a complete electrical circuit of an oscillator similar to the oscillator loop shown in FIG. As shown in equation (7), the resonance of a mechanical resonator (such as the resonant membrane 110) is equivalent to the equivalent inductance represented by the electrical element resistor R _B , capacitor C _B and inductor L _B in FIG. , Where R _B is proportional to the mechanical damping of the membrane 110, C _B is proportional to the mechanical stiffness of the membrane 110, and L _B is the mechanical mass of the system. Is proportional to The series RLC connection may be represented by the equation of motion as described above and is in parallel with the feedthrough capacitance C _ft formed by the membrane in combination with a plane below the membrane 110 (eg, ground plane 130). The transimpedance amplifier TIA can be regarded as a current controlled voltage source (CCVS) having a gain M. Therefore, TIA / CCVS converts the incoming current to voltage v _in, the current resonance circuit R _B, and C _B and L _B, parallel flow to the parasitic feedthrough C _ft, capacitor C _ft is This is necessary because there is capacitive crosstalk between the membrane 110 and the ground plate 130 separately from the mechanical resonance. CCVS phase shift is assumed to be _{constant, C ft // R B -C B} -L B branch across the phase shift may be constant in order to satisfy the oscillation conditions (due to Barkhausen stability determination). Since the phase shift constant, which follows the relationship between the value and the vibration frequency of the R _B -C _B -L _B. Thus, when a magnetic field is applied to the circuit 400 (representing the compass 100 using the membrane), the magnetic field changes the equivalent resistance R _B , resulting in a phase shift within the oscillator loop 400 that shifts the oscillation frequency proportionally. To do. For example, if R _B , C _B, and L _B change by a ratio Δ, the vibration frequency of the exemplary circuit 400 changes (depending on the relationship between the magnetic field and the vibration frequency), thereby causing the feedthrough capacitors C _ft and R _B, and interaction with C _B and L _B occurs. The vibration frequency may be measured as an output to determine the magnetic field using the calculations described herein.

次に、ω_０が次式（１５）として定義される。

また、Ｑが次式（１６）として定義される。

ωがω＝ω_０＋Δω（式（１７））として定義される場合、Δω≪ω_０と仮定すると、アドミタンス（式（１４））は、次式（１８）として書き換えられうる。

アドミタンスの位相は、実数項と虚数項の比が一定になるように一定でよい（式（１９））。

ここで、Ｑ≪１と仮定すると、式（１９）は、更に、Ｒ_Bに対する微分（次式（２１））をとる次式（２０）として単純化されてもよく、Δωは、Ｒ_Bの変化を振動周波数の変化に関連付けられる。

FIG. 5 shows a plot of the admittance (which is 1 / impedance) of the resonator 110 in the imaginary plane. The admittance of the resonator is expressed by the following equation (14).

Next, ω ₀ is defined as the following equation (15).

Q is defined as the following equation (16).

If omega is defined as ω = ω ₀ + Δω (equation (17)), assuming Derutaomega«omega _0, admittance (Equation (14)) can be rewritten as the following equation (18).

The phase of the admittance may be constant so that the ratio of the real term to the imaginary term is constant (formula (19)).

Here, assuming that Q«1, formula (19) may further be simplified as a differential equation which takes the (equation (21)) (20) with respect to R _B, [Delta] [omega is the R _B The change is associated with a change in vibration frequency.

For a frequency close to the resonance frequency ω ₀ , the real part (1 / R _{B, α 1} , 1 / R _{B, α 2} ) of the admittance on the x axis is changed to the imaginary part (ω _α1 C _ft , ω _α2 C of the RLC branch on the y axis. When plotting against _ft ), a circle intersecting the resonance points ω _α1 , ω _α2 can be plotted. Each point of the circle that intersects ω _α1 and ω _α2 corresponds to the frequency ω, and when ω increases, the circle turns clockwise, so when the frequency is swept, the plot becomes a circle. The circle may be moved along the imaginary axis by an amount equal to the feedthrough admittance jωC _ft when plotting the total admittance. In the oscillator loop, the admittance phase is fixed by the phase of the amplifier gain M, as shown by the straight line 510 intersecting the origin in FIG. If the resonant circuit 400 is disposed in a magnetic field, the element R _B, the value is changed in C _B and L _B, a circle will expand (e.g., circle intersects the omega _{[alpha] 2)} or shrinkage (for example, a circle Intersects ω _α1 ). The angle at which the line intersects the x-axis is equal to the M phase shift. The intersections ω _α1 and ω _{α2 of the} fixed phase line 510 and the circle set the vibration frequency. The oscillator may lock at a frequency corresponding to a point on the circle that is in fixed phase. The fixed phase line 510 indicates the resonance frequency (intersections ω _α1 and ω _α2 between the fixed phase line and the circle plot indicate the resonance frequency). When the circle plot expands or contracts, the intersections ω _α1 and ω _α2 move with respect to each plot circle to represent the frequency shift of the vibration. The detuning factor δ changes the diameter 520 of the circle. Thus, since the detuning coefficient δ shifts the vibration frequency, the fixed phase lines intersect with the admittance circle intersections ω _α1 and ω _α2 differently.

Therefore, in summary, a change in the direction of the magnetic field with respect to the magnetometer 100 changes the Lorentz force F _lor acting on the membrane 110, thereby changing the equivalent impedance R _{B and} changing the vibration frequency (formula (21)). reference).

  Table 1 below shows the characteristics of an exemplary membrane as currently used in several pressure sensor applications. These membrane parameters are merely examples, but these parameter values can be used to indicate the magnitude of the vibration frequency shift. Various parameters may be used to realize the membrane, and the values change from each other by a simple scaling law, for example, if the membrane size is doubled, the resonant frequency is halved. The mass is doubled and the rigidity is halved. The metal membrane size and manufacturing may vary somewhat, but the exemplary membranes in Table 1 are exemplary sizes for low cost, simplicity of manufacture, and integration with CMOS.

The change in vibration frequency of the exemplary membrane of Table 1 can be derived by calculating an admittance circle as described above. For example, if the admittance is calculated when the alternating current flows parallel to the magnetic field (circle intersecting ω _α1 ) and perpendicular to the geomagnetic field (circle intersecting ω _α2 ), the change in diameter is about 1%. Is calculated to be The amplifier phase may be fixed at a value of, for example, 60 degrees, thereby fixing the vibration frequency and allowing a frequency shift to be calculated as a result of changes in the circle diameter 520. Thus, a 90 degree rotation of the earth's magnetic field shifts the vibration frequency by 50 ppm, which is within the resolution of most frequency measurement systems.

  The intersection of the fixed phase line 510 and the circle indicates the vibration frequency and shifts when the circle diameter changes as a result of the change in the magnetic field direction.

In view of the foregoing, the measurement of the direction of the magnetic field can be understood in connection with the movement, displacement or movement of the membrane 110 in response to the Lorentz force F _lor generated by the magnetic field, bias voltage and current. FIG. 6 shows a cross section of one winding of a coil 620 that may be embedded in a metal mechanical membrane 610 (open), the coil being shown embedded in a substrate 630. The supply current i begins at the current source 640 in the substrate 630 and flows into the wire mass m embedded in the membrane 610 and continues to flow into the wire coil loop after passing through the resistor R in the substrate 630. As will be appreciated by those skilled in the art, since the membrane 610 is a spring / mass system 600, the membrane 610 has a mass m, a stiffness k, and a damping coefficient γ. Assuming that the magnetic field B is in the plane of the membrane 610 following the surface of the wafer, the Lorentz force F _lor pulls the membrane 610 down from the plane as shown. In addition, the membrane will be subjected to the mechanical noise brown (random) force F _noise as described above.

この結果、次式（２２）が得られる。

地球磁場Ｂ₀を測定するために、全磁場Ｂを生じるコイルによって引き起こされる磁場の影響をなくすように計算が行われる。したがって、図２Ａに関してＮ×ｌ×ｉ_in×Ｂとして前述したローレンツ力Ｆ_lorは、次式（２３）又は次式（２４）として表されることがある。

外力Ｆ_lor及びＦ_noiseを受ける質量／ばね系６００において、運動方程式ｘは、次式（２５）として得られる（系に与えられることがある周波数である、電流ｉに与えられる周波数ωと共に変化する項だけを検討する）。

式（２５）で分かるように、運動方程式は、地球の磁気力Ｂｏだけに関して導られることがあるので、コイルの磁場は、メンブレン６１０の変位ｘを測定することによって考慮されうる。コイルによって自己生成された磁場の周波数が、地球磁場によって生成された磁場の周波数と異なっており、したがって、図示されたようなＢ₀の測定値と無関係になりうることに注意されたい。 Note that in some embodiments, if the required measurement is a geomagnetic field, the magnetic field generated by the coil itself may also be considered. The total magnetic field B affecting the membrane 610 may be generated by both the earth magnetic field B ₀ and the following equation, which is the magnetic field of the coil.

As a result, the following formula (22) is obtained.

In order to measure the earth's magnetic field B ₀ , a calculation is performed so as to eliminate the influence of the magnetic field caused by the coil producing the total magnetic field B. Therefore, the Lorentz force F _lor described above as N × l × i _in × B with respect to FIG. 2A may be expressed as the following equation (23) or the following equation (24).

In the mass / spring system 600 subject to external forces F _lor and F _noise , the equation of motion x is obtained with the following equation (25) (which varies with the frequency ω applied to the current i, which is a frequency that may be applied to the system: Consider only the term).

As can be seen in equation (25), the equation of motion can only be derived with respect to the earth's magnetic force Bo, so that the magnetic field of the coil can be taken into account by measuring the displacement x of the membrane 610. Note that the frequency of the magnetic field self-generated by the coil is different from the frequency of the magnetic field generated by the earth's magnetic field and can therefore be independent of the B ₀ measurement as shown.

最後に、Ｆ_noise（以下式）によって提供される追加の変位が、前述のような信号対雑音比を提供することに注意されたい。したがって、ローレンツ力Ｆ_lorを計算しＦ_noiseを考慮することによって、地球磁場Ｂ０の角度αを決定できる。

As described above, the magnitude of the Lorentz force F _lor depends on the angle between the magnetic field and the membrane sheet or electric wire embedded in the membrane. As a result, the current flowing in the x direction is the current flowing in the y direction. _Flor depends on the angle of the magnetic field relative to the membrane angle α, as it causes detuning of different vibrational frequencies. The displacement of the wire or membrane 610 is maximized at its resonant frequency. The maximum displacement x _pk of the membrane 610 at the resonance frequency ω ₀ may be expressed as the following equation (26) (Q multiplied by force divided by the spring constant k, Q and the number of wires N, membrane (and Therefore, the product of the length l of each coil of the wire), the earth's magnetic field B0, and the current flowing through the wire i is divided by the spring constant k of the membrane).

Finally, note that the additional displacement provided by F _noise (below) provides a signal-to-noise ratio as described above. Therefore, the angle α of the geomagnetic field B0 can be determined by calculating the Lorentz force F _lor and considering F _noise .

The minimum Lorentz force F _lor that can be detected by the exemplary membranes 210, 610 shown with respect to FIGS. 2A and 6 is the mechanical detection limit of the mass / spring system 600 when the magnitude of random noise exceeds the Lorentz force. Determined by. In other words, the sensor is at the limit of detection when the random noise is equal to the Lorentz force. As a specific example, the mechanical detection limits of exemplary membranes 210, 610 are shown, where the number of windings N is 90, the loop depth d is 5 μm, the length l of the membranes 210, 610 is 220 μm, the current i Is 1 mA root mean square (rms), resistance R is 1 kΩ, bandwidth Δf is 4 Hz, Lorentz force F _lor is 8.4 × 10 ⁻¹⁰ N, noise force F _noise is 1.0 × 10 ⁻¹² N, displacement x 9.9 × 10 ⁻¹² m (about 10 picometers) and a mechanical detection limit of 25 nT / Hz ^1/2 (25 nano-tesla per square root Hz). In comparison, a Hall compass sensor has a noise floor of 100 nT / Hz ^1/2 and is therefore not as sensitive as a compass using the metal membrane described herein.

In order to measure the displacement of the membrane 610 and thus the magnetic force B0 as described above, the displacement x may be measured electrically. FIG. 7 shows a cross section of the membrane 610 with respect to the electrode 720 on the substrate 740 and below the membrane 610. The electrode 720 may be a plate held at a potential V _bias at a gap distance g from the membrane 610, and capacitively coupled to the plate 720 and the membrane 610 by a capacitance C that generates a measurable displacement current (closeness to the voltage V _{by bias} ).

ノイズ電流ｉ_noiseは、電流の帯域幅、メンブレンの剛性及びバイアス抵抗Ｒ_Biasの大きさに依存し、以下式として表されうる。

ノイズの影響を最小にするために、以下式として表されることがある抵抗Ｒ_Biasを最大にすることが望ましい。

電流が、Ｒ_BiasとＣのインピーダンスに通されるとき、これらのインピーダンスは、本明細書で述べるようなＢ０を決定するために測定されうる出力信号ｖ_sense（メンブレンの変位によって生成される出力電圧）を生成する。本明細書で述べたように、メンブレンサイズｌ^２、ギャップのサイズｇ及びローレンツ力Ｆ_lorのキャパシタンスＣは既知なので、値ｘ（変位）とＣ（キャパシタンス）の出力読取り値ｖ_senseが計算されうる。Ｒ_Biasがきわめて大きいことがあり、従って、バイアス電圧と、キャパシタンスの変位導関数と、キャパシタンスに正規化された変位とを掛けたものに等しいｖ_senseは、以下式として表されることがある。

FIG. 8 shows an exemplary circuit that is electrically equivalent to the system of FIG. As can be seen in FIGS. 7 and 8, the two displacement current sources i _sense (output current generated by the membrane displacement) and i _noise are the Lorentz force F _lor and the random noise F _noise that cause the membrane 610 to be displaced by the distance x. These two currents i _sense and i _noise are caused to flow through the bias resistor R _bias , and a capacitance C is generated by the plate of the membrane 610 and the plate of the electrode 720. The current generated by the displacement of the Lorentz force F _lor and hence the capacitance C may be expressed as:

The noise current i _noise depends on the current bandwidth, the rigidity of the membrane, and the magnitude of the bias resistance R _Bias and can be expressed as:

In order to minimize the effects of noise, it is desirable to maximize the resistance R _Bias which may be expressed as:

When current is passed through the impedances of R _Bias and C, these impedances are the output signal v _sense (the output voltage generated by the membrane displacement, which can be measured to determine B0 as described herein. ) Is generated. As described herein, since the membrane size l ² , the gap size g and the capacitance C of the Lorentz force F _lor are known, the output readings v _{sense of} the values x (displacement) and C (capacitance) can be calculated. . R _Bias can be quite large, and therefore v _sense equal to the bias voltage, the displacement derivative of the capacitance, and the capacitance multiplied by the normalized displacement may be expressed as:

Note that for detection, v _sense may be amplified by amplifier 730, which introduces an electrical noise v _{noise amp} in addition to the electrical noise v _nise generated by the circuit. However, exemplary calculations show that the effect of electrical noise can neglect the detection limit of the sensor compared to mechanical noise. Amplifier noise may be expected to be greater than random system noise. In an exemplary membrane 610 having a length l of 220 μm, a gap g of 500 nm, a bias voltage V _{bias of} 10 v, a bandwidth Δf of 4 Hz, and an amplifier noise of an exemplary amplifier of v _{noise, amp} of about 20 nV rms, the capacitance C is 860 fF, resistance R _bias >> 200 kOhm, and peak sensor voltage v _sense , peak = 200 V, and the electrical detection limit is ² nT / Hz ^1/2 (2 nano-Tesla per square root Hz). As described above, the mechanical detection limit is 25 nT / Hz ^1/2 , and the combination is hardly different from only mechanical noise as shown in the following equation.

  In accordance with the above, various exemplary embodiments have been described in detail, by providing a metal membrane mounted on a CMOS-based magnetometer that detects the phase shift of an oscillator that includes the membrane, at an inexpensive and versatile shape factor. A manufactured magnetometer is provided.

  From the foregoing, it will be apparent that various exemplary embodiments of the invention may be implemented in hardware and / or firmware. Moreover, various exemplary embodiments may be implemented as instructions stored on a machine-readable storage medium that may be read and executed by at least one processor to perform the operations detailed herein. . A machine-readable storage medium may also include any mechanism for storing information in a form readable by a machine, such as a personal or laptop computer, server, or other computing device. Accordingly, machine readable storage media may include read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, and similar storage media.

  Those skilled in the art will appreciate that the block diagrams herein represent conceptual diagrams of illustrative circuits that implement the principles of the invention. Similarly, any flowcharts, flowcharts, state transition diagrams, pseudocode, etc. may be expressed in substantially machine-readable media, and thus various processes performed by a computer or processor, such computer or processor specified. It will be understood to represent whether or not.

  Although various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, the invention allows other embodiments and the details can be modified in various obvious respects. Please understand that. It will be readily apparent to those skilled in the art that variations and modifications can be made within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not limit the invention, which is defined only by the claims.

100 Magnetometer device 110 Metal membrane 130 Fixed plate 150 Membrane grounding

Claims (21)

A feedback loop configured to vibrate the metal membrane, the feedback loop comprising an amplifier and a voltage bias connected to a first input of the metal membrane (110);
A membrane ground (150) connected to the membrane output;
A fixed plate (130) including a first fixed plate output connected to a second input of the amplifier, wherein the fixed plate (130) is physically separated from the metal membrane (110); on the other hand, it is capacitively coupled before Symbol metal membrane (110), wherein the physical separation is different by the angle of the magnetic field (B) with respect to the direction of the current,
Second fixing plate output sensitive to Lorentz force (F _lor),
A magnetometer device (100), connected to the second fixed plate output, comprising a Lorentz force (F _lor ) and a circuit for calculating an angle of magnetic force based on a shift of a vibration frequency of the metal membrane.   The magnetometer device according to claim 1, wherein the metal membrane further includes a continuous metal sheet.   The magnetometer device according to claim 1, wherein the metal membrane further includes a continuous metal winding extending in parallel lines from the membrane input to the membrane output.   The magnetometer device according to claim 3, wherein the metal membrane further includes an insulator sheet in which the metal winding is embedded. The metal membrane is
An equivalent electrical inductance proportional to the mechanical mass of the metal membrane;
An equivalent capacitance proportional to the mechanical stiffness of the metal membrane;
An equivalent electrical resistance proportional to mechanical braking of the metal membrane;
The magnetometer device according to claim 1, comprising:   The magnetometer apparatus according to claim 1, wherein the amplifier includes a current control voltage source.   The magnetometer device according to claim 6, wherein the current control voltage source has a gain.   The magnetometer device according to claim 1, wherein the metal membrane is a self-supporting type.   The magnetometer device according to claim 1, wherein the fixing plate is fixed to a substrate.   The magnetometer device according to claim 1, wherein the fixing plate is fixed to a wafer. A magnetometer device (100) for measuring the orientation of the device,
An oscillator including a metal membrane (110) and a feedback loop;
A processor;
With
The feedback loop is
An alternating current is passed through the metal membrane (110) to vibrate the metal membrane (110),
Generate capacitive displacement current,
Sending the capacitive displacement current to an amplifier in the feedback loop;
Amplifying the capacitive displacement current by the amplifier;
Configured to send the amplified current as a voltage to the metal membrane;
The processor is
The shift in oscillation frequency caused as the feedback loop by said metal membrane (110) is measured,
Based on the shift and the current direction of the vibration frequency, and is configured to calculate the angle of the external magnetic field with respect to the current direction, the magnetometer (100). The magnetometer device according to claim 11 , wherein the vibration frequency is a mechanical resonance frequency of the metal membrane. A fixed ground plate,
The magnetometer device of claim 11 , configured to generate a bias voltage between the metal membrane and the fixed ground plate. The magnetometer device of claim 13 , wherein the processor is connected to the fixed ground plate to measure the vibration frequency shift. The magnetometer device according to claim 13 , wherein the fixed ground plate is separated from the metal membrane. The magnetometer device of claim 11 , wherein in calculating the external magnetic force angle, the processor is further configured to negate a vibration frequency detuning effect. The magnetometer device of claim 16 , wherein the processor is further configured to subtract one or more current direction vibration frequencies when canceling a vibration frequency detuning effect. The magnetometer device of claim 11 , wherein the processor is further configured to filter interference from vibrations of the metal membrane. The magnetometer device of claim 18 , wherein the processor is further configured to measure the frequency of the oscillator for a sufficient period of time. A magnetometer device (100) for measuring the orientation of the device,
An oscillator comprising the metal membrane (110) and a feedback loop;
A processor;
With
The feedback loop is
An alternating current is passed through the metal membrane (110) to vibrate the metal membrane (110),
The processor is
The measured shift in the oscillation frequency caused by the feedback loop and the metal membrane (110),
Based on the shift and current direction of the vibration frequency, to calculate the angle of the external magnetic field with respect to the current direction,
A magnetometer device (100) configured to cancel the vibration frequency detuning effect by subtracting the vibration frequency in one or more current directions when calculating the angle of the external magnetic field. A method for measuring the orientation of a device,
Passing an alternating current through the metal membrane (110);
Generating a capacitive displacement current;
Sending the capacitive displacement current to an amplifier;
Amplifying the capacitive displacement current by the amplifier;
Sending the amplified current as a voltage to the metal membrane;
Measuring a shift of the oscillation frequency of said metal membrane (110),
Based on the shift and current direction of the vibration frequency, the method comprising the steps of: calculating the angle of the external magnetic field with respect to the metal membrane (110).

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